The present disclosure is for a self-aligning rifle bullet offering better accuracy and aerodynamic performance. Increasing the long-range accuracy of rifle bullets is a subject well represented in the prior art. Much of the prior art is directed to adjustments in the rifle. Other prior art proposes changes to the bullet. Following is a brief discussion of accuracy problems that still remain unresolved by current or prior art solutions.
The French Army adopted the first aerodynamically designed long-range rifle bullet known as the “Balle D” bullet in 1898 for an 8×50 mmR Lebel smokeless powder service cartridge. The Balle D bullet was a lighter weight, spire pointed, boat-tailed rifle bullet made of a monolithic brass alloy. It could fly faster and farther than the earlier round nosed, heavy for caliber, cupro nickel jacketed, lead cored bullets it replaced. By 1906, every major army had adopted the version of this more aerodynamic bullet. These were the first generation tangent ogive bullets, and they have been the accepted norm for best accuracy in rifle shooting at all ranges. In fact, the majority of current standard issue target rifles use a 1.5-degree throat angle originally optimized for firing these tangent ogive bullets.
In the mid 1980's, ballistician William C. Davis developed a secant ogive boat-tailed Very Low Drag (VLD) bullet design. The purpose of the invention was to serve as a more efficient long-range target rifle bullet. Many of the current accurate long-range rifle bullets are characterized as this second generation jacketed and lead cored VLD bullets. However, with current VLD bullets, riflemen have discovered two major problems—each stemming from what is known as in-bore yaw.
In-bore yaw occurs during firing when long nosed, short bodied, secant ogive bullets become canted at an angle to the bore of the rifle upon engraving of the bullet by the bore rifling. Once this happens, the bullet becomes off balance. Current VLD bullets are not designed to correct themselves during the remainder of their trip through the barrel and therefore the resulting trajectory of the bullet is altered. The impairment in the trajectory causes variability in target impact points. Moreover, the in-bore yaw causes the center of gravity (CG) of these VLD bullets to shift laterally off the bore axis and fly with rather large initial coning angles. These problems degrade the long-range accuracy of the bullet and result in an increased atmospheric drag and crosswind sensitivity than what is intended by the original design.
In response to the in-bore yaw and static imbalance problems associated with these jacketed, lead-cored VLD bullets, many long rang target shooters have chosen to select redesigned barrels. The purpose of the redesigning the rifling of the rifle barrel is to provide the slowest possible barrel twist rates. This is done in an effort to marginally stabilize their VLD match bullets. Unfortunately, one side effect of a lower barrel twist rate is a decrease in the gyroscopic stability (Sg) of the fired bullets. This tradeoff results in instability of the fired bullets at long ranges.
Recognizing the shortcomings of selecting barrels having slower twist rates, other shooters have opted to make adaptations to the bullet design. One popular design is known as the Berger Hybrid Ogive bullet design. This Berger Hybrid Ogive bullet design is a variant of a VLD design utilizing a modified head shape. The ogive-generating curve of a bullet is the calculated curvature of the nose of the bullet. In this context, the base portion of the ogive of Berger hybrid bullet is a type of tangent ogive, while the remainder of the hybrid ogive is a shortened secant ogive design ending in a rather large diameter (0.15 caliber) blunt meplat. Although somewhat effective at managing the VLD accuracy problem, much of the aerodynamic advantage of using a secant ogive versus a tangent ogive nose shape has been traded away in this dual ogive design, i.e., the Berger Hybrid design only improves the VLD style bullet guidance problem at the front end of its dual ogive, while the rear portion of the bullet is still free to shift around within the necessary case neck and ball seat clearances.
Current solutions do not completely satisfy the VLD accuracy problem, but instead result in a give and take—gaining accuracy in some areas while losing aerodynamic efficiency in others. The present invention provides a much better solution. The present invention reduces or eliminates in bore yaw, thereby allowing shooters to select faster barrel twist rates and achieve greater accuracy at longer ranges, while also solving the shifting problem inherent to the Berger Hybrid Ogive bullet design.